This is a simple idea, add new structures made out of random blocks that endermen can pick up, and then have them spawn there more often. This is a good idea because endermen are really rare, so having a place where they spawn more often would be helpful. They also make sense, since endermen are intelligent creatures like humans, as mentioned in the mobestiary.
I hope you like the idea!
If you are looking for endermen, go to the End.